toolchain/gcc: disable makeinfo

Newer versions of texinfo (>=5) break the gcc makeinfo routine, so just
disable it.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Tested-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>